1. Field of the Invention
Exemplary embodiments of the present invention generally relate to a cleaning unit, an image carrier unit, and an image forming apparatus, and more particularly, to a cleaning unit used in an image forming apparatus such as a copier, a facsimile machine, and a printer, and an image carrier unit that includes the cleaning unit.
2. Discussion of the Related Art
Cleaning units are generally used to remove toner remaining on a surface of a photoconductor after transfer of a toner image therefrom. A blade-type cleaning unit, which is one type of cleaning unit, is known to remove toner with an elastic blade that is made of rubber material.
However, a drawback of blade-type cleaning units is that, when the elastic blade and the photoconductor contact each other with low adhesion, the toner removed from the surface of the photoconductor by the elastic blade is allowed to pass between the surface of the photoconductor and the elastic blade, markedly decrease cleaning ability of the cleaning unit.
To prevent such a drawback, the elastic blade is pressed more or less strongly against the photoconductor, at high contact pressure. However, the high contact pressure to abut the elastic blade against the photoconductor can warp the elastic blade, which can cause a streak-like or a band-shaped cleaning failure. Therefore, it is difficult to maintain stable cleaning performance of the cleaning unit, and in the long term abrasion of a surface film formed on the photoconductor is increased, reducing the service life of the photoconductor.
Recently, high image quality is increasingly demanded, and consequently the size of toner particles used in the developers used to develop images therefore tends to be reduced. Further, reductions in toner manufacturing costs and an increase in a transfer rate of toner are also demanded, and thus an image forming apparatus using spherical toner particles (hereinafter also simply “spherical toner”) has been commercialized in which the spherical toner is obtained by forming pulverized or amorphous-shaped toner into a spherical shape using a polymerization method. It is known that use of such small-sized and spherical toner causes cleaning performance to be inferior to that of the pulverized toner in the blade-type cleaning unit.
As a different cleaning unit, an electrostatic cleaning unit employing an electrostatic cleaning method is also used. To perform the electrostatic cleaning method, the electrostatic cleaning unit includes a conductive cleaning member that slidably contacts the surface of the photoconductor and applies a voltage to the conductive cleaning member so as to remove toner from the photoconductor by using electrostatic force as well as sliding frictional force. The electrostatic cleaning unit can achieve good cleaning performance when cleaning the small-sized toner or spherical toner and prevent mechanical sliding contact with the photoconductor to reduce the abrasion of the surface film of the photoconductor.
Further, the above-described electrostatic cleaning unit may include a roller-type cleaning member or cleaning roller that also serves as a conductive cleaning member. In addition to the cleaning roller, a conductive elastic blade may be disposed upstream from a portion where the cleaning roller contacts the photoconductor in a direction of movement of the surface of the photoconductor. The conductive elastic blade is held in contact with the photoconductor and is supplied with a voltage having a polarity opposite that of the cleaning roller.
Residual toner on the surface of the photoconductor has a wide distribution of polarized particles thereon, and therefore the residual toner, which is charged to the same polarity as the cleaning roller, cannot be removed only with a cleaning member to which a voltage of one polarity is applied. However, with the above-described electrostatic cleaning unit, residual toner remaining on the surface of the photoconductor even after the transfer operation receives a charge from the elastic blade when passing a portion where the cleaning blade contacts the photoconductor. Thus, the charged state of the toner may become the same as that on the elastic blade and the opposite of that on the cleaning roller, which is hereinafter referred to as a “toner polarity control.” The above-described toner polarity control can efficiently remove the residual toner that has reached a contact position of the cleaning roller and the photoconductor using the cleaning roller, which is supplied with a voltage having a polarity opposite that on the elastic blade.
Although providing good cleaning performance for the small-sized toner or spherical toner, the electrostatic cleaning method cannot remove large amounts of toner all at once, which can result in poor cleaning performance. However, in the above-described electrostatic cleaning unit, the elastic blade is held in contact with the cleaning roller at an upstream side in the direction of movement of the surface of the photoconductor. That is, after the elastic blade has mechanically cleaned the surface of the photoconductor, the cleaning roller may clean the surface thereof. By so doing, the amount of toner conveyed to a portion at which the cleaning roller removes the toner can be reduced, and therefore, even when a large amount of toner is conveyed to the portion, good cleaning performance can be obtained.
A related-art image forming apparatus that employs the above-described cleaning unit applies a voltage to the elastic blade from a power source provided in a main body of the related-art image forming apparatus via a blade supporting member that fixes the elastic blade to the main body of the related-art image forming apparatus. The blade supporting member that is used in such image forming apparatus may be conductive and have high rigidity. The elastic blade supported by the blade supporting member may include a portion that is fixed to the blade supporting member and another, second portion continuous or not with the first portion that is not fixed and freely extends from an end of the blade supporting member to a leading portion thereof contacting the surface of the photoconductor. Whereas the fixed portion is not elastically flexible, the free portion deforms flexibly.
When the free portion is too short, flexible deformation of the elastic blade may be reduced, making the elastic blade incapable of absorbing a tolerance in a gap between the photoconductor and the elastic blade and unable to contact the photoconductor along the axis of the photoconductor, which may degrade the cleaning performance by the elastic blade. If the cleaning performance of the elastic blade degrades, the amount of toner conveyed to the cleaning position of the cleaning roller increases. Since a large amount of toner cannot be removed by the electrostatic cleaning method all at once, poor cleaning performance can be the result. If the gap tolerance is reduced to adapt to an elastic blade that includes a shorter free portion and smaller amount of flexibility, precision of both component dimensions and assembly of the elastic blade and the photoconductor may need to be increased, necessitating increased cost.
Further, as volume resistance of the conductive elastic blade decreases, the voltage of a power source that applies a voltage to the elastic blade can be lowered. However, when an elastic blade that has an extremely low volume resistance is used and the photoconductor has an electrical pinhole on the photoconductor, a current may be supplied from the elastic blade to a base body of the photoconductor via the pinhole. If the current moves from the elastic blade to the base body, the elastic blade cannot be charged, which prevents toner polarity control. Therefore, the elastic blade may need to have a certain minimal volume resistance. As an electrode that applies a voltage to the elastic blade having a certain minimal volume resistance becomes closer to the portion where the elastic blade contacts the photoconductor, the voltage of the power source that applies the voltage to the elastic blade can be set to a lower value.
However, as described above, when a voltage is applied to the elastic blade via the blade supporting member, the blade supporting member may be an electrode to apply the voltage to the elastic blade. If an end portion of the blade supporting member that serves as an electrode is set to become closer to the contact position of the photoconductor and the elastic blade, the free length of the elastic blade may become shorter. With this structure, maintenance of an acceptable level of cleaning performance may lead to an increase in cost.
The above-described problem is not limited to instances in which a photoconductor is a target member to be cleaned by the cleaning unit, but can occur when a target member is any member with a moving surface to which toner can adhere, for example, an image carrier, which includes an intermediate transfer member, and a recording medium conveyance member that conveys a recording medium.
Further, the above-described cleaning unit employs the cleaning roller as a conductive cleaning member, but is not limited thereto. For example, the above-described problem may occur when the cleaning unit employs a cleaning brush that has brush fibers applied with a certain voltage and held in contact with a target member to be cleaned so as to electrostatically remove toner.